The overall objective is to investigate the involvement of transfer RNA in amino acid regulation and to determine the functions of tRNA modifications in this regulation. To fulfill this objective the following approaches will be applied: (1) Characterize the Salmonella typhimurium mutants isolated as having altered regulation of several amino acid biosynthetic pathways to determine if the pleiotropic phenotypes are caused by lesions affecting tRNA maturation. This will include the purification of the mutant tRNA, acylation and chromatography of the tRNA to detect changes in quantity or migration patterns, and biochemical analysis to determine the composition of modified tRNA bases. (2) Isolate new pleiotropic regulatory mutants by selecting strains resistant to several structurally unrelated amino acid analogs. Use genetic techniques, such as conjugations and transductions, to locate the sites of these mutations relative to other markers on the S. typhimurium linkage map. (3) Examine the consequences of the tRNA alterations on the regulation of amino acid biosynthetic pathways by measuring the levels and repressibility of several enzymes representative of these pathways. Continue these physiological experiments for amino acid pathways not previously investigated to determine whether tRNA is involved in their control.